Method of making a low mass foam electrical structure

ABSTRACT

A method of making an electrical structure having a foam housing is set forth. The foam housing includes an interior surface forming a conductive cavity adapted to carry energized waveforms therethrough. An electrical component of the electrical structure is integrally formed with the interior surface as the foam housing of the structure is assembled. The method includes the steps of depositing a plating material into a mold, pouring a foam polymer into the mold and removing the plated foam structure from the mold without etching the section from the mold. The method further includes steps of forming a metallic form into a planar structure, filling the open pores of the foam with a material such as photo-resist, machining a cavity from the foam, electroplating the cavity in the foam then removing the photo-resist material.

STATEMENT OF RELATED CASES

This application is a divisional application of U.S. Ser. No. 15/013,551filed Feb. 2, 2016 entitled “LOW MASS FOAM ELECTRICAL STRUCTURE” andthis application is a divisional application of U.S. Ser. No. 13/315,590filed Dec. 9, 2011 entitled “LOW MASS FOAM ELECTRICAL STRUCTURE” andclaims priority to provisional application U.S. Ser. No. 61/459,323entitled “LOW MASS RF STRUCTURES (LMRS)”, filed Dec. 10, 2010, theentireties of which are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to foam electrical structures for transmittingsignals.

BACKGROUND OF THE INVENTION

Modular structures have been developed for transmitting signals for awide variety of electrical systems. Such structures are typicallyprovided in a system to achieve a required system function, such as, forexample, to direct, redirect, attenuate, combine or spread signals toone or more desired locations.

Modular structure fabrication for electrical systems can be complicatedby inherent drawbacks, such as cost, temperature tolerances, size,compatibility, connectability, and structural complexity. The resultingstructures frequently require multiple components to achieve a modularstructure. Also, prefabrication requirements can substantially inhibittransportation and portability of the resulting structures. Cumbersomestructures for directing signals are not suitable for a number ofapplications, such as portable applications or space applications.Additionally, temperature considerations can affect the usefulness ofthe structures.

SUMMARY OF THE INVENTION

In accordance with the principles herein, an electrical structure havinga foam housing is set forth. The foam housing includes an interiorsurface forming a conductive cavity adapted to carry energized waveformstherethrough. An electrical component of the electrical structure isintegrally formed with the interior surface as the foam housing of thestructure is assembled.

The foam housing can include a suitable organic or metallic foam suchas, for example, ECCOSTOCK® FPH, aluminum foam or any other suitablelightweight material. The foam housing of the electrical structure caninclude a first housing section and a second housing section. Theelectrical component can be integrally formed during a fusing of thefirst housing section to the second housing section.

Any suitable electrical structure, such as, for example, a waveguide canbe formed in accordance with the principles herein. An electricalstructure formed in accordance with the present principles can include,for example, a suspended conductor, a strip-line conductor, a coaxialconductor, a combiner, a splitter or any other suitable structure.

A lightweight modular housing for dissipating heat contained inenergized waveforms passing therethrough can be formed in accordancewith the principles herein. The housing can be formed of any suitablematerial, such as, for example, at least one of a metallic foam and anorganic foam. The housing can further include an electrical componentintegrally formed with an interior surface of the housing.

Examples of suitable electrical components include, but are not limitedto, for example, a suspended conductor, a strip-line conductor, acoaxial conductor, a combiner, a splitter or any other suitablestructure.

A low mass electrical structure constructed in accordance with theprinciples herein can include a heat dissipating foam material firsthousing section. A heat dissipating foam material second housing sectioncan also be provided, if needed, to increase the cooling capabilities ofthe structure. The second housing section can be adapted and constructedto couple to the first housing section. An electrical component can bejoined to an interior surface of at least one of the first housingsection and the second housing section of the low mass electricalstructure.

The first housing section of the low mass structure can include acavity. The electrical component can be joined to at least one of theinterior surface of the cavity and the interior surface of the secondhousing section.

The second housing section of the low mass structure can also include anidentical cavity to the cavity of the first housing section.

The electrical component can be joined to interior edge surfaces of thefirst and second housing sections.

The electrical component can include a conductor, a strip-lineconductor, a coaxial conductor joined to the interior surface via aconductor suspension mechanism, and/or at least one of a filter, anamplifier, and a combiner.

In an embodiment, a low mass structure having an electrical componentcan include a combiner connected to a center conductor to form acombination, the combination joined to the interior surface via acombination suspension mechanism.

A method in accordance with the principles herein can include providinga first housing section made of foam. The method can further includeproviding a second housing section made of foam. The method can alsoinclude fusing the first housing section to the second housing sectionto form a fused housing, while encapsulating an electrical componentwithin the fused housing, wherein the electrical component is joined toan interior surface of the housing.

Thus, in accordance with the principles herein, a lightweight waveguidemodule for transmitting signals therethrough can be formed of a heatdissipating foam outer structure.

The lightweight waveguide module can further include an encapsulatedconductive channel.

In an embodiment, the lightweight waveguide module can include anelectrical component integrally formed within the module.

The electrical component of the lightweight waveguide module can furtherinclude at least one of a filter, an amplifier, and a combiner.

The lightweight waveguide module can be formed of a metallic foam.

A lightweight module for transmitting electromagnetic energy in therange of dc to several THz formed of a suitable material, such as ametallic foam or laminate can also be constructed in accordance with theprinciples herein.

The lightweight module can further include a lightweight insulatingexterior and a plated conductive interior channel.

The lightweight module can further include a center conductor.

The center conductor of the lightweight module can include a strip-lineconductor.

A method according to the principles herein can include depositing aplating material into a mold. For example, a foam polymer can be pouredinto the mold to form a plated foam section for a structure. The platedfoam structure can be removed from the mold without etching the sectionfrom the mold. The mold can be formed with stainless steel, for example.The plating material can be selected from the group consisting ofsilver, copper, and gold, or from any other metal with the exception oftitanium.

Unique structures are realizable in accordance with the principlesherein due to the materials and assembly methods set forth.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of exemplary embodiments of the concepts set forth herein willbecome apparent from the description, the claims, and the accompanyingdrawings in which:

FIG. 1 is a sectional view of an exemplary lightweight structure.

FIG. 2 is a perspective view of an exemplary embodiment of a structure,wherein a waveguide and a coaxial transmission line are bothincorporated into a single structure.

FIG. 3 is a perspective view of an exemplary embodiment of a structureincluding a transmission line and an encapsulated cavity.

FIG. 4 is a perspective view of an exemplary embodiment of a structureincluding a waveguide and an encapsulated cavity.

FIG. 5 is a top view of an exemplary embodiment of a structure includinga six-way beam splitter.

FIG. 6 is an exemplary embodiment of a structure encapsulatingcomponents for a waveguide and a microstrip.

FIG. 7 is a sectional view of an exemplary embodiment of a connectorstructure.

FIG. 8 is a sectional view of an exemplary embodiment of a backplanestructure.

FIGS. 9a-9e illustrate steps for fabricating exemplary open-corestructure.

FIG. 10 illustrates an exemplary embodiment of an open-core structurewith a supported center conductor.

FIGS. 11a-11c illustrate steps for fabricating an exemplary centerconductor.

FIG. 12 illustrates an exemplary structure incorporating a suitablecylindrical profile conductor.

FIG. 13 illustrates yet another embodiment of an exemplary structureincorporating a suitable cylindrical profile conductor.

FIG. 14 illustrates an exemplary embodiment of a structure encapsulatinga suitable linear taper transition element.

FIG. 15 illustrates an exemplary embodiment of a structure encapsulatinga suitable reduced depth of cut round profile taper transition element.

FIG. 16 illustrates graphically simulations of insertion loss data forthe exemplary structures of FIGS. 14 and 15.

FIGS. 17a-17d illustrate exemplary connector transitions for anembodiment of an exemplary structure.

FIG. 18 illustrates graphically performance simulations of the variousexemplary connectors of FIGS. 17a -17 d.

FIG. 19 illustrates an exemplary structure including a co-axial air lineformed with a rounded center conductor suspended by a thin,low-dielectric element.

FIG. 20 illustrates graphically simulations of the loss per inch of atransmission line through the co-axial air line formed as shown in FIG.19.

FIG. 21 illustrates graphically simulations of the loss of thetransmission line plus the loss of transitions from a coax to aconnector of a 6″ coaxial line.

FIG. 22 illustrates an exemplary embodiment of a structure including aco-axial air line with increased via diameter compared to the exemplarystructure of FIG. 19.

FIG. 23 illustrates graphically simulations of the resulting insertionloss obtained with the modified via diameter of FIG. 22.

FIG. 24 illustrates an exemplary structure encapsulating a waveguideformed with a suspended dielectric therein.

FIG. 25 illustrates graphically simulations of waveguide loss per inchachieved in an exemplary waveguide structure with and without thedielectric element of FIG. 24.

FIG. 26 illustrates an exemplary embodiment of an electrical structurewith an internal electrical component applied to multiple combinablesections of the structure.

FIG. 26a illustrates an exemplary embodiment of an electrical structurewith an internal electrical component applied to one combinable sectionof the structure and an electrical component sandwiched betweencombinable sections.

FIG. 27 illustrates an exemplary embodiment of an electrical structureincluding combinable sections configured to form a waveguide.

FIG. 28 illustrates an exemplary embodiment of an electrical structureincluding a suspended conductor on a dielectric.

FIG. 29 illustrates an exemplary embodiment of an electrical structureincluding a strip line conductor on a dielectric.

FIG. 30 illustrates an exemplary embodiment of a structure encapsulatinga suspended conductor.

FIG. 31 illustrates an exemplary embodiment of a structure encapsulatingan electrical component.

FIG. 32 illustrates an exemplary embodiment of a structure encapsulatinga suspended combiner center conductor.

FIG. 33 illustrates an electrical structure shown generally at 3300,wherein an active electrical component, such as, for example, a combineris encapsulated within the electrical structure; and

FIG. 34 illustrates an exemplary embodiment, wherein an activeelectrical component such as a filter or an amplifier, is encapsulatedwithin an electrical structure.

DETAILED DESCRIPTION

A method and/or structure in accordance with the principles hereinprovides for the realization of unique structures, such as low loss, lowmass precision microwave, millimeter wave, RF structures, modularstructures and modular components or other suitable structures.

In accordance with the principles herein, suitable modules, such as, forexample, hermetic modules, non-hermetic modules, backplanes/baseplates,RF structures, transmission lines and beam forming networks (BFN) orbeam steering networks (BSN), or any other suitable structure can beformed overcoming the lack of flexibility and difficulties in formationof known structures.

For example, hermetic modules can be formed that can include active orpassive components embedded internally, such as, for example, coaxialinputs, outputs, and/or interconnects; waveguide inputs, outputs, andinterconnects with hermetic windows; combinations of coaxial andwaveguide inputs, outputs, and/or interconnects; embedded absorbingmaterials; embedded magnetic materials; embedded dielectric materials;embedded thermally conductive materials; multiple modules stacked in theZ direction with coax or WG interconnects; and/or multiple modules in aplane with hermetic and/or non-hermetic interconnects.

Any suitable combination of elements defining a hermetic module,constructed in accordance with the principles herein, can also beapplied to a suitable non-hermetic module, with the obvious exceptionthat the non-hermetic module would not be sealed. A non-hermetic modulecan further include components mounted externally to alamination/housing, such as, for example, WLP (wafer-level packaging),BGA (ball grid array), etc.; and/or waveguide and/or coaxialinput/out/interconnects without hermetic windows, or any other suitablecombination of elements.

Further, suitable backplanes or baseplates can be constructed inaccordance with the principles herein. These structures can be laminatedto strong structural supporting layers formed of, for example, solidmetal, or, for example, to other modules, or to any other suitablestructure. They can further include routing of RF and non-RF signalsfrom one module to another or from a module to any other suitablereceiving structure.

Additionally, suitable RF modules or structures, such as, for example,transmission lines, filters, resonant cavities, waveguide structuresincluding magic Tees, splitters, hybrids, filters, couplers ordirectional components, coaxial splitters and combiners, or any othersuitable RF structure can be achieved in accordance with the principlesherein.

Moreover, a beam forming network (BFN) and/or a beam steering network(BSN) can be formed in accordance with the principles herein, whereinmodules can be selectively adhered to each other and/or to otherstructures to form the BFN and/or the BSN.

Structures constructed in accordance with the principles herein canserve functional roles in the transmission of signals, such as, forexample, transmission, attenuation, isolation, load termination,filtration, and radiation to name a few. For example, waves havingelectromagnetic energy between DC and several THz, wherein the energylevel is defined by the waveguide size, conductor size, and othervarious factors, can be transmitted wherein propagation of the waves iscontrolled and conducted, at least in part, by a structure configured inaccordance with the principles herein.

Further, signals can be attenuated based on a predetermined reduction inamplitude of electromagnetic energy between DC and several THz, at leastin part, by a structure configured in accordance with the principlesherein.

Signals can also be isolated, i.e., coupling prevented, between morethan one electromagnetic field between DC and several THz, at least inpart, with a structure constructed in accordance with the principlesherein. Additionally, load termination, filtration, or reduction inamplitude, and the direction and polarization of radiation generatedwithin the structure can be controlled by selecting components andstructural features to achieve these objectives.

In accordance with the principles herein, a wide variety of modules,such as an embodiment of a module illustrated generally at 100 in FIG. 1can be formed. The module 100 is formed of a suitable lightweightmaterial, such as a lightweight metal or organic foam, and can becombined with other modules and/or components for forming a BFN, BSN, orother structure, such as, for example, a transmission structure. Firstand second lightweight sections 110, 120 can include inner conductivesurfaces 130, 140. When the sections 110, 120 are brought together by asuitable method, such as, for example, by fusing, a conductive cavity150 is formed therein. The conductive cavity 150 can be configured tocarry energized signals therethrough such as, for example, when theconductive surfaces 130, 140 are adapted to integrate upon combining thesections 110, 120 to form an electrical component 160 suitable forconducting signals, and/or for forming a beam transmitting network.

Various other embodiments, not limited to the configurations or purposeof the illustrated modules and structures, such as module 100illustrated in FIG. 1, that are suitable for forming laser transmissionnetworks can be formed in accordance with the principles herein. Onesuch embodiment, for example, is a module shown generally at 200 in FIG.2, formed and adapted to accommodate both a suspended waveguide 220 andcoaxial transmission line 210 in a lightweight shell housing. A suitablehousing material for the module 200 can include, for example, a metallicfoam, such as aluminum foam, or any other suitable lightweight material,such as a non-metallic lightweight material with conductive materialselectively applied, such as by plating or depositing, or by any othersuitable method, where electrical conduction is needed.

In another embodiment, a module constructed to accommodate a coaxialtransmission line 310 can be provided, such as, for example, the moduleshown generally at 300 in FIG. 3 in accordance with the principlesherein.

In yet another embodiment, a module, illustrated generally at 400 inFIG. 4, can include, for example, a waveguide transmission line 410 forconducting signals to a cavity 420. The cavity 420 can also beconfigured to accommodate an electrical component, such as, for example,a Microwave Monolithic Integrated circuit (MMIC) Chip.

In still another embodiment, a six-way beam splitter can be constructedsuch as, for example, a module shown generally at 500 in FIG. 5 inaccordance with the principles herein. The module 500 can includecoaxial lines 510, operatively connected to a six-way beam splitter 520.The coaxial lines 510 can be secured to the module 500 with coaxialconnectors 530. The module can include a lightweight foam inner core 540formed about the components of the module 500, or through which thecomponents can be assembled, wherein, for example, the foam core isprefabricated to accommodate assembly of the components, such as thecoaxial lines 510. Alternatively, the module 500 can be formed in asuitable plated mold such as, for example, a stainless steel mold, orany other suitable mold.

A module constructed in accordance with the principles herein caninclude, for example, a waveguide 610 to microstrip transition 620formed of a suitable lightweight material as illustrated generally, forexample, at 600 in FIG. 6.

A module constructed in accordance with the principles herein can form aconnector, such as, for example, a connector shown generally at 700 inFIG. 7. The connector 700 can include a coaxial input 710, a waveguideoutput 720, and a thermal dissipation device, such as, for example, acopper slug 730 operatively connected to the coaxial line and thewaveguide line.

As illustrated in FIG. 8, an embodiment of a backplane moduleconstructed in accordance with the principles herein is shown generallyat 800. The backplane module 800 includes a main body portion 810. Themain body portion 810 can include, for example, laminates such as afirst laminate 820 and a second laminate 830. The first and secondlaminates can be formed of a suitable material, such as, for example,carbon laminates, or circuit board laminates. A transmission line 860for RF signals can be formed through the first laminate 820 and the mainbody portion 810 for routing RF signals from a first device 840 to asecond device 850, or vice versa. In this embodiment, the backplanemodule 800 serves to both route the RF signals and as a structuralelement.

FIGS. 9a through 9e illustrate an embodiment of lamination of solid andopen-core materials in accordance with the principles herein. Asillustrated in FIG. 9a an open core module 900 can be provided in afirst step. The open cores of the module 900 can then be filled with anysuitable material, such as, for example, machining waxes, polyesters andphoto resists as illustrated in FIG. 9b . In one embodiment, the photoresist is an epoxy-base negative photo resist such as SU-8. The fillingmaterial both provides stability for machining the open core materialand facilitates electroplating. It is subsequently removed as shown inFIG. 9d . The module 900 can then be machined to form one half or acoaxial structure as shown in FIG. 9c . Plating 910 can be applied tothe machined module, as illustrated in FIG. 9d . A completed module canthen be formed by connecting another module 920 which has been processedin the same way to the module 900, wherein a supported center conductor930 is connected to the plating 910 to form a module assembly 1000,shown in an exploded view, for example, in FIG. 10.

In yet another embodiment, a suitable supported center conductor can beformed, for example, as illustrated in FIGS. 11a-11c . First, a printedcircuit board 1100 or other suitable structure, such as a housing,frame, or heat sink, can be provided with vias connecting top and bottomtraces. Next, silver plating can be applied to the printed circuit board1100 in FIG. 11b . The silver can then be plated up to form acylindrical profile conductor 1110, as illustrated, for example, in FIG.11 c.

FIG. 12 illustrates an embodiment wherein a suitable cylindrical profileconductor, such as the profile conductor 1210 is incorporated into asuitable module, such as the module shown generally at 1200. The profileconductor 1210 can be formed of a suitable material, such as, forexample, silver, copper, gold or any other suitable material orcomposite on, for example, a printed circuit board 1220. The module 1200is formed of a suitable material, such as a first metallic foam section1240 and a second metallic foam section 1250. One suitable metallicfoam, for example, is aluminum foam. Plating can be provided along themodule, such as plating 1230, and can be formed of a suitable materialor composite, such as silver. Vias 1260 can be included to providefunctionality for the device.

Alternatively, a module 1300 formed of a suitable metal or organic foamcan include a center conductor 1310 formed on a dielectric 1320. Aconductive surface 1330 is formed within a first organic foam section1340 and a second organic foam section 1350. Further, recesses 1370 areprovided within the second organic foam section to accommodate a pcboard formed of a dielectric 1320 and vias 1360.

In accordance with the principles herein two types of taperedtransitions from a coaxial line to a microstrip transmission line areshown in FIGS. 14 and 15 respectively. FIG. 14 depicts a moduleillustrated generally at 1400 which can provide an exemplary, effectivetransition from a coaxial line 1420 to a microstrip transmission line1430 with a suitable taper transition, such as, for example, a conicallinear taper transition of an outer conductor 1410, as illustrated inFIG. 14. The conical linear taper transition with unequal radius outerconductor cones yields the highest performance in operation. It is alsodifficult to make this version of a tapered coaxial transition.

Alternatively, a reduced depth of cut round profile taper transition1510 can adequately provide a suitable coaxial to microstrip transition,as illustrated with a module shown generally at 1500 in FIG. 15. Thetransition 1510 is easier to manufacture, but of lower performance thanthe conical linear taper of the outer conductor, as shown graphically inFIG. 16 which uses a finite element method solver for electromagneticstructures to depict the achievable performance of the structures ofFIGS. 14 and 15. In particular, FIG. 16 shows the loss (in dB) per inchof transmission through structures when operated at differentfrequencies (in GHz). The structure of FIG. 14 is shown as a solid linewhile the structure of FIG. 15 is shown as a dashed line. Moderateperformance can be achieved with the embodiment of FIG. 15 below 30 GHz.

Further, achieving an efficient connector transition from a coaxialair-line to a suitable coaxial connector, such as, for example, an MSSSconnector, or a connector specification, can be achieved in a number ofways. A few exemplary embodiments are illustrated in FIGS. 17a-17d .FIG. 17a depicts a straight connection. This transition has a largediscontinuity resulting in poor performance. A linear-linear tapertransition is shown in FIG. 17b . This transition is achieves a moderateperformance level as shown by the solid line in FIG. 18. FIG. 17cdepicts a spherical-linear transition exhibits poor performance, asshown by the dashed line of FIG. 18. Finally, FIG. 17d depicts aspherical-bullet taper which shows a superior performance in FIG. 18.

As illustrated in FIG. 19, a module 1900 can include a co-axial air lineformed with a rounded center conductor 1910 suspended by a thin,low-dielectric element, such as, for example, a printed circuit board1920. An outer conductor of the air line is formed by machining andplating a top half 1930 and a bottom half 1940 of the module 1900.

The performance of structures achievable with the present invention hasbeen simulated using a finite element method solver for electromagneticstructures. FIG. 20 illustrates graphically an exemplary chart of theloss (in dB) per inch of transmission through the co-axial air lineformed as shown in FIG. 19 when the co-axial line is operated atdifferent frequencies (in GHz). In other words, FIG. 20 depicts howstrong of an electrical propagation the structure of FIG. 19 cansupport.

FIG. 21 illustrates the loss (in dB) of the transmission line plus theloss of transitions from a coaxial to a connector of a 6″ coaxial line.An alternative embodiment is shown in FIG. 22, with increased viaspacing and consequently the via diameter as compared to the structurein FIG. 11a in a structure shown generally at 2200. Similarly to FIG.20, FIG. 23 depicts loss per inch (in dB) per frequency (in GHz) of theembodiment of FIG. 22.

Further, in accordance with the principles herein, a waveguide, such as,for example, a WR-22 (Q-band) Waveguide 2400, illustrated in FIG. 24,can be simulated using the same construction technique as the coaxialair-line of FIG. 19. Similarly to FIGS. 20 and 23, FIG. 25 illustratesgraphically the WR-22 waveguide loss (in dB) per inch per frequency (inGHz) for both embodiments having a dielectric inside the waveguide,shown as a solid line, and for embodiments without a dielectric insidethe waveguide, shown as a dashed line.

In accordance with the principles herein, aluminum foam, or othersuitable metallic foam or other low-density cellular or non-cellularorganic or inorganic rigid bulk material, can be employed inmicrowave/millimeter wave applications in place of known, heavysupporting structures. As a result, the weight of such structures, aswell as the loss/frequency dispersion, is drastically reduced forbeam-forming networks (BFN) constructed in accordance with the aboveprinciples. Further, cage structures that can serves as backplanes forunits to be inserted in modules can be formed in accordance with theprinciples herein.

A number of varied structures can be formed, and can serve to formnetwork modules for transmitting signals, or can interface with otherunits. In other words, other technologies, such as Wafer Level Packaging(WLP) can be accommodated according to the principles herein. Further,all structures that are possible with microstrip can be achieved, andcan realize a very low insertion loss as well. Thus, both weight andcost are significantly reduced in accordance with the principles herein.

Further, the amplification needed to overcome the loss of phased arrays,as they mature, is substantially reduced in accordance with theprinciples herein. All manner of microwave circuits can be realized in avery low loss medium. When the material includes foam or hascharacteristics of a foam, the porous nature of the material eliminatesscattering off the surface, thus minimizing reflections in a cavity. Asa result, lighter, less expensive boards with reduced transmission lossare achieved.

In accordance with the principles herein, lightweight material, such asfoam, serves as a useful structure for low loss RF propagation. Further,using a very thin, low dielectric board results in a coaxial structurehaving near true coaxial transmission lines characteristics, and isfurther supported by a very strong, lightweight material. This isparticularly important given the long distances traveled by a largearray BFN.

In accordance with the principles herein, structures suitable forvarious modes of signal transmission can be realized for electromagneticwaves of frequencies between DC and several THz, such as, for example, aplanar transmission line between two ground planes, separated by adielectric (stripline); a planar transmission line between two groundplanes, separated by air (suspended stripline); a planar transmissionline with one ground plane separated by a dielectric (microstrip); aplanar transmission line with one ground plane separated by mostly air(suspended microstrip); a slot line; a fin-line; a coaxial transmissionline with round, oval, rectangular or square profile; a waveguide withround, rectangular or oval profile; ridged waveguides; coplanarwaveguides; beam waveguides; DC connections; and dielectric loadedwaveguides, or any other suitable or desired signal transmissionstructure, where light weight and low loss are desired structuralcharacteristics for signal propagation.

Numerous suitable applications of the principles herein can be achieved.For example, low loss transmission lines (waveguides, coaxial, etc. aslisted above); controlled loss transmission lines (attenuators);terminations; housings for electronic circuits; housings for electroniccircuits that function as DC and RF interconnects as well; mechanicalmounting structures for modules; mechanical mounting structures formodules that also function as DC and RF interconnects; housings forelectronic circuits featuring selectively absorptive sections; housingsfor electronic circuits featuring a high degree of electrical shielding;housing for electronics that allow for cooling through the flow of gasor liquid coolant through the structure; fluid/gas transport integratedinto electronics housings; antenna structures including, but not limitedto horns, reflectors, shaped surfaces; antenna structures withintegrated housings for electronics; arrays of antennas; covers forelectronics housings; radomes; radomes with integrated electronicshousings or metalized elements; true time delay lines; rotman lens;frequency selective surfaces; mechanisms for routing optical fibers;filters; resonant structures; cavities for oscillators; magic teehybrids; mechanical waveguide switches; transitions between waveguidetypes (round, rectangular, elliptical); transitions from waveguide tomicrostrip; transitions from microstrip to coaxial; and transitions fromcoaxial to waveguide, to name a few.

A method of forming modules such as a compact housing, transmission lineor other structure can include forming a structure from a lightweightsupport material, such as a metallic foam or laminate. The structure canbe formed by, for example, molding a shape, stamping, molding a polymerfoam to a plate, or any other suitable method. Stamp mold metalizedsponges could be formed of a coated foam, for example, in accordancewith the principles herein.

The structure can be filled with, for example, a temporary filler. Forexample, the structure can be filled to support a resulting foam orsemi-foam structure while machining, or to provide a desirable surfaceconfiguration for plating. The structure can be machined to form astructure, such as a housing or a transmission line, for example. Thestructure can be plated with electrically conductive materials, forexample, or insulating material, when needed. Further, plating can beemployed to create smooth surfaces for signal propagation andselectively keep exposed irregular surfaces, which reduces cavitymoding. Filler material can, for example, be removed after plating toreturn the medium back to an ultra light weight configuration, or, wherea light filler material is used, to accommodate the formation ofconnecting members or transmission lines, and/or connections. Further,additional materials, such as, for example, absorbers, resist or anyother suitable material can be deposited to, for example, an irregularfoam surface constructed in accordance with the principles herein.

In accordance with the principles herein, structures can be formed usingpourable foam materials, preformed foam plates, or any other suitablefoam structure. For example, one exemplary method for forming astructure can include electroplating a suitable mold, such as, forexample, a stainless steel mold or a mold formed of any other suitablematerial with a suitable plating material, such as, for example gold,silver, copper or most metals other than titanium, to form a platedmold. A polymer foam mixture can then be poured into the mold. Thepolymer foam mixture adheres to the plating, but can be lifted directlyfrom the mold without requiring an etching step to remove the mold fromthe foam and plating.

Additional steps can include, for example, installing additionalcomponents, laminating pieces together to form units, modules and/orhousings. Further, parts can be attached in and on the structure, suchas for example, by laminating two halves together with, for example, asuitable adhesive, a solder, diffusion bonding, or any other suitablemethod. Further, finline components can be laminated into the structure,if desired.

Where the support material is, for example, a lightweight foam, an opencell polymer can be metalized to achieve similar performance metrics asa metallic foam, for example.

A porous foam further includes inherent thermal properties that can beachieved by flowing air through the material, or by using the materialwhere a natural air flow is present, such as at high altitudes. Anorganic foam can provide desired insulating properties for a structure.Further, a thermal medium can be driven through the structure duringoperation for controlling temperature characteristics, such as, forexample, air or a suitable fluid, such as water or a coolant, inaccordance with principles of thermodynamics and avionics.

Structures formed in accordance with the principles herein can takeadvantage of using a suitable preformed foam, such as, for example, asuitable organic or metallic foam. Open cell metallic foams in the rangeof a 10% density factor for materials, such as aluminum, provide lightweight structures with adequate mechanical stiffness and good platingadhesion surfaces. The open cell construction of these foams enables RFmode suppression surfaces for fragmenting RF cavity modes. Likewise,organic materials such as, for example, ECCOSTOCK FPH® provide goodstrength to weight ratios, as well as good adhesion to plating andproperties suitable post plating. Materials need to withstandtemperatures above 150° C. and pressures of 300 psi for bonding of thehalves. Electrical components can be formed on a surface of the foam,and selectively fused, as desired, to one or more additional pieces offoam which may or may not also have an integrated electrical structure,as illustrated, for example, by an exemplary electrical structure showngenerally at 2600 in FIG. 26.

The electrical structure 2600 includes a first foam section 2610 formedof a suitable foam material, and a metallic coating 2620 can be formedthereon. The metallic coating 2620 can take on a partial coatingcharacteristic when applied using deposition techniques, such asmasking, or by applying preformed metal sheets, adhered by heating tothe structure. A second foam section 2630, formed of a suitable foammaterial, can be provided, and selectively fused to the first foamsection 2610, either directly or indirectly, to form an internalelectrical component 2640. The internal electrical component 2640 isthus integrally formed with the electrical structure 2600 where the foamforms an external boundary of the electrical component 2640, and wherethe conductive surface of the internal electrical component 2640 isformed by combining the foam sections 2610 and 2630. The second foamsection 2630 can also include a metallic coating or preformed sheet thatserves as a component of the electrical component 2640. Alternatively,as shown in FIG. 26a , the first foam section 2610′ can sandwich a metalplate 2650′ between the first and second foam sections 2610′ and 2630′,where the second foam section 2630′ has a metallic coating or preformedmetal sheet applied to an internal surface 2660′ of the second foamsection 2630′. Such an embodiment may be useful where it is desirablefor different foams to be employed for the first and second foamsections.

As illustrated in an exemplary embodiment shown in FIG. 27, a suitablewaveguide structure, shown generally at 2700, can be formed by combininga first foam section 2710 with a second foam section 2730. Each of thefirst and second foam sections 2710 and 2730 can include a waveguidechannel 2720 and 2740, respectively. The waveguide channels 2720 and2740 can be formed by forming a channel in the foam, such as by cuttingthe foam, or by fusing foam sections of varied cross section together.The waveguide channels 2720 and 2740 can be plated with preformed metalplates, or by applying a metallic coating using a suitable process, suchas painting or a metallic deposition process. The waveguide channelwithin the waveguide structure 2700 is formed by fusing the first foamsection 2710 to the second foam section 2730 such that the waveguidechannels 2720 and 2740 are aligned to one another.

As illustrated in the exemplary embodiment shown in FIG. 28, a suspendedconductor 2860 can be integrally formed with a conductive channelstructure shown generally at 2800. The conductive channel structure 2800includes a first foam section 2810 having a conductive interior surface2820. A second foam section 2830 is provided, and includes a conductiveinterior surface 2840. A plate 2850 can be provided that spans a channel2870 of the second foam section 2830 and a channel 2880 of the firstfoam section 2810 when the first and second foam sections 2810, 2830,respectively, are fused together. A number of varied embodiments thatvary the plate position can be utilized to render the interior surfaceconductive. The plate 2850 can be formed of any suitable material toboth satisfy the electrical requirements of the conductive channelstructure 2800, and to directly or indirectly insure adhesion of thesuspended conductor 2860. Suitable plates 2850 can include, for example,any plate upon which a metal can be directly or indirectly plated toachieve desired electrical characteristics of the conductive channelstructure 2800.

As illustrated in the exemplary embodiment shown in FIG. 29, astrip-line conductor 2960 can be provided on a suitable plate 2950disposed between first and second foam sections 2910 and 2930,respectively. The first and second foam sections 2910 and 2930 are thenphysically combined. Once the first and second foam sections 2910 and2930 are combined, a conductive channel structure shown generally at2900 is formed. Here, ends 2970 and 2980 of the strip-line conductor canbe seated in recesses 2985, 2990 of a conductive surface 2940 of thesecond foam section 2930.

FIG. 30 illustrates an exemplary embodiment of a conductive channelstructure shown generally at 3000. The conductive channel structure 3000includes a first foam section 3010 and a second foam section 3030. Thefirst foam section 3010 and the second foam section 3030 are adapted andconstructed for connecting together to form an internal electricalstructure, such as, for example, by fusing. To this end, conductivesections, in the form of, for example, metal plates or metallic coating3020 and 3040 are provided in the first and second foam sections 3010and 3030, respectively, of the conductive channel structure 3000. Acoaxial center conductor 3050 can be provided in a channel 3060 in thestructure 3000, formed by fusing the first foam section 3010 to thesecond foam section 3030. To this end, the conductor can be suspendedwithin the channel 3060 using a conductor suspension mechanism, such as,for example, one or more foam sleeves 3070, or suspended by a plateprovided between the first and second foam sections 3010 and 3030, or byan other suitable structure for suspending the center conductor 3050within the channel 3060 formed by fusing the first foam section 3010 tothe second foam section 3030.

In the exemplary embodiment of FIG. 31, an active electrical element3150 is provided in a cavity of a conductive chamber 3160 formed in afoam electrical structure shown generally at 3100. The electricalelement 3150 is encapsulated within the conductive chamber 3160. Theconductive chamber 3160 is formed by providing a metal coating on arecess 3120, 3140 formed in first and second foam sections 3110 and3130, respectively and connecting the first foam section 3110 to thesecond foam section 3130 such as, for example, by fusing. Coaxialtransmission lines 3170 transmit signals to and from active electricalelement 3150

FIG. 32 illustrates an exemplary embodiment of an electrical structureshown generally at 3200. The structure 3200 includes a combiner centerconductor 3250. The combiner center conductor is suspended within achannel 3260 formed by connecting a first foam section 3210 to a secondfoam section 3230. Metal layers 3220 and 3240 are integrally formedwithin the structure 3200 by electrically connecting, such as, forexample, by fusing the first foam section 3210 to the second foamsection 3230. Alternatively, other suitable components, such as, forexample, a beam splitter could be incorporated into the electricalstructure 3200.

FIG. 33 illustrates an electrical structure shown generally at 3300,wherein an active electrical component, such as, for example, a combiner3350 is encapsulated within the electrical structure 3300 byelectrically connecting a first foam section 3310 with a second foamsection 3330 of the structure 3300. The combiner 3350 is adapted andconstructed to transmit combined signals received from first and secondconductors 3360 and 3370, respectively, to a third conductor 3380. Aconductive inner surface 3320, 3340 is provided within each of the firstand second foam sections 3310, 3330.

FIG. 34 illustrates an exemplary embodiment, wherein an activeelectrical component 3450, such as a filter or an amplifier, isencapsulated within an electrical structure shown generally at 3400. Theelectrical structure 3400 includes a first foam section 3410 and asecond foam section 3430. A conductive layer is provided on an internalsurface of the first foam section 3410 to form a conductive inner layer3420. A conductive layer is provided on an internal surface of thesecond foam section 3430 to form a second conductive layer 3440. Theelectrical component 3450 is encapsulated within the electricalstructure 3400 when the first foam section 3410 is electricallyconnected to the second foam section 3430.

Numerous applications and advantages can be achieved for wavepropagation and for general structural formation in accordance with theprinciples herein, and the examples and figures set forth are merelyexemplary of the numerous possibilities for device construction.

We claim:
 1. A method of manufacturing a low mass radio frequency (RF)transmission line structure comprising the steps of: forming first andsecond housings of open cell metallic foam; filling the open cellmetallic foam with a filling material; machining a first cavity in afirst surface of the first housing and machining a second cavity in afirst surface of the second housing; plating the first and secondcavities; removing the filling material from the open cell metallic foamforming the first and second housings; locating a printed circuit boardcomprising an electrical component between the first and secondhousings; and coupling the first surface of the first housing to thefirst surface of the second housing so that the first and secondcavities are aligned and form the RF transmission line structure.
 2. Themethod of claim 1 wherein the filling material is a photo resist.
 3. Themethod of claim 2 wherein the filling material is an epoxy-basednegative photo resist.
 4. The method of claim 1 wherein the fillingmaterial is a machining wax.
 5. The method of claim 1 wherein thefilling material is a polyester.